Was just thinking about this... I've heard certain cars have put a motor on each wheel, which seems like an engineering headache to me, but has anyone linked multiple motors up in tandem for a single very high-torque output? I would think that if you could rig it up reliably that pumped into a high gear ratio you could achieve some very high speeds as well as a solid low-end. Links? Info?

If you check MetricMind's website (www.metricmind.com), they sell the Brusa ASM810 motor I mentioned before. This is a 3PAC motor, and it's made flat on each end. It's designed to be "stackable" with itself, so for more power, you can add additional motors. (And of course, a pile of money.) I think the armature shaft is at least partially hollow, so you can wind up with several motors all driving the same shaft.

The Brusa is just one example, but I'm sure any motor maker can come up with a configuration that allows motor stacking this way.

The problem I have with the idea of wheel-hub motors is the large amount of unsprung weight. If you're going to go with a motor per wheel in a normal passenger vehicle, it would be better to have the motors inboard, in the chassis, then have drive shafts and CV joints going to the wheel. This is for handling and ride quality.

That thought occurred to me as well Robert, but I have yet to see it done. It sounds to me like a viable solution to overcoming the lack of torque inherent with smaller motors if one wants to go with a direct drive setup through a gear reduction differential.

I guarantee you a belt would slip with high-power motors. You'd need a very heavy chain or even a geared setup. What I think would work well is a triangle of motors each with a small gear (maybe 15 teeth) attached to the output shaft, then a large gear in the center of the 3 with an output shaft in the center where the power of all 3 is transferred. I'd draw that up but don't have the time right now.

Side note - I forgot how the motors respond to series vs parallel wiring. I know it has something to do with the weakest one and balancing output but unbalanced draw.

You have right idea for the belt, is not a great idea, gears are better.
If you connect the shaft of two motors. It is obvious they are connected in series. Like this the same current pass through the two motor and theirs torque are equal. If you connect in parallel, the difference between internal resistances generates waste. One motor wants to run faster than the other and the other brakes the first.

I spend a little time to draw the twoo schematics for serie or parallel wiring of twoo DC motors.
I hope have time one day to explain the benefit of serie connection for connected safts.
Serie - parallel wirring of DCs motors.

Her you are:
The math show that in serie n the speed of shaft is capable to be the same for the twoo shafts without wast.
In parallel mode n1 is not equal to n2 then it work not at the optimum.